Electronic crystal oscillators are widely used as clock pulse sources for various electronic circuits. The crystal of such an oscillator is a piezoelectric material precisely dimensioned in a configuration in which it may be caused to oscillate at its natural frequency by the application of a driving voltage pulse. For some applications the crystal may be in the shape of a rod, typically having either a round or a square cross-section. For other applications, it may be in the shape of a thin wafer. Regardless of the particular shape, the crystal must be held in a manner which permits it to vibrate freely in its natural frequency mode, while at the same time providing support for it and electrical connections to its electrodes.
An oscillator crystal which is of the thin wafer type has an electrode layer on each face. It must be held in such a manner that it may freely vibrate in the drum-head mode. This is usually accomplished by suspending the wafer between the ends of two resilient metal terminals arching upwards from the edges of a circuit. An edge contact area of the wafer is soldered or otherwise conductively bonded to the end of each of the terminals at diametrically opposed perimeter locations. The structure then has its natural frequency tuned to a predetermined value by the addition of a layer of tuning material in its central region. The layer of tuning material may be in the form of added thickness evaporated on the central region of an electrode layer.
The attachement of a crystal wafer to a circuit and its subsequent tuning is a delicate manual operation which is relatively costly. Different diameter wafers suitable for different requirements generally call for corresponding adaptations in the mounting hardware. A low profile, rugged structure is desireable. Imprecise location of the wafer on the circuit requires individual alignment of the tuning layer applications equipment for each assembly process. Excessive stress at the joint between the terminals and the wafer can lead to stress fracturing, either as a result of handling or from excessive sympathetic oscillations of the terminals themselves.
There is therefore a need for an improved mounting assembly for the crystal wafer of electronic crystal oscillators.